There are a variety of insects that cause major economic losses in agriculture and spread diseases among plants. Whitefly is one of the most notorious agricultural pests in the world. For example, in 1981, the sweet potato whitefly, Bemisia tabaci (Gennadius), caused 100 million US dollar damage in cotton, cucurbits, and lettuce in the United States. In 1986, whitefly became a problem in Florida where B. nahaci caused approximately US$2 million of damage to Florida's US$8 to 10 million poinsettia crop.
Whitefly is now known to feed on more than 500 different plants. For example, sweet potato, tomato, beans, cotton, carrot, cassava, squash, lettuce, pepper, egg plant, watermelon, and cucumber are all known hosts to the pest. It is also known that sweet potato whitefly may transmit more than 70 diseases caused by virus and microorganisms.
Silverleaf whitefly (B. argentifolii Bellows and Perring) was first found in Taiwan in 1991. In 1995, silverleaf whitefly was responsible for 1000 hectares of agriculture losses in Taiwan.
Whitefly is very difficult to control with conventional pesticide application. Many factors contribute to the lack of control obtained with pesticides. Only few commercially available pesticides are effective against whiteflies. However, these pesticides are only effective if care is taken in a very thorough application several times a week. In addition, whiteflies spend most of their life on the undersides of leaves; therefore, growers must adjust their management practices to permit increased pesticide coverage there. The spacing of the plants must be such that the chemical spray can penetrate the canopy and reach all surfaces of the plants.
Further, the ineffective use of the chemical pesticides may be costly, and has other significant drawbacks, such as the pollution to the environment, and the potential health hazards to agricultural workers and to consumers.
Therefore, safer and more effective methods for controlling whiteflies are needed. Although biological control agents have been studied for years, to date no biological control agent has been commercially successful for the control of whiteflies.
U.S. Pat. Nos. 4,942,030 and 5,413,784 disclosed the utilization of fungi Paecilomyces fitmosoroseus and Beauveria bassiana in controlling sweet potato whitefly.
Streptomyces sps. have been widely used in the production of antibiotic materials. However, thus far, no Streptomyces sp. had been identified as having biopesticidal activity against whiteflies.